Technical Abstract:
Organic N released in soil by roots is mineralized by microbes to be recycled in roots. The dynamics of this N mineralization-immobilization turnover between corn roots and microbes was quantified by the model NCSWAP/NCSOIL with data from corn field plots. The kinetics of inorganic N-15 in the 0- to 15- and 15- to 30-cm soil layers and organic N-15 in the above-ground corn was documented for 10 years of continuous corn fertilized with 20 and 200 kg NH4+-N ha-1 enriched with 8.0 kg N-15 ha-1 (4.0 and 40.0 atom-% N-15, respectively). N-15 was added for 5 consecutive years, then stopped to obtain relaxation kinetics. Residues were not returned to allow full impact of roots and root exudation on the system's dynamics. The soil was rototilled. The experimental kinetics are presented. Gross and net rates of the processes underlying these kinetics as described by the model are discussed.